Looks like an older post but perhaps the OP is still interested in opinions here. What is your goal for the lift?
What you are describing is one of the many techniques for increasing ones bench press lift. A power bench press would be much as you have described. The arch in the back has several effects to the lift. The first is to reduce the ROM of the lift. By arching your back you are able to move your chest higher from the bench and thus have a shorter distance to lower the weight to touch. The second effect is that it will align your body in such a way to place more emphasis on the chest and less on the deltoids. The chest is a lot larger muscle and capable of moving more weight than the deltoids. The third would be to allow your lats to be activated more during the low end of the lift. And finally the arch in the back allows for for transfer of leg drive into the lift. At the low end of the lift you would push your heels into the floor which can transfer through the more rigid position of the arched spine.
As far as hand spacing, that too is yet another technique used to increase ones lift. Typically the wider you go outside of shoulder width, the more you will activate the deltoids and to some degree the pecs. The closer the hands are inside of shoulders width, the less the deltoids and chest are activated and the more the triceps are called into play. I find that I have more power right at shoulders width apart or index finger around the inner knurling ring. The trick is to find the position that best lets you put as much power into the bar from all three if lifting more weight is your goal.
Now that brings me back to my original question what is your goal for the lift? There is certainly some benefit to be gained by lifting a heavier weight through technique but the benefit will be distributed over a greater number of muscles in the chain. This is a good thing except when your focus for the lift is specific to chest development. If you are also doing plenty of other exercises for deltoid and tricep development then perhaps the barbell bench press is not the best choice. "What the @#$%! is Wildman saying!? Dont bench press?" No, but the power bench press it is not the most productive lift for chest development in my opinion. You would be better served using a slightly wider grip with little arch in your back to place emphasis on the chest than to do the power version. Even a dumbell press or fly is more effective for directly stimulating the chest area specifically.
This all boils down to your goals for the lift and what kind of program you are on. In a fullbody layout then sure, use the benchpress and even go with the power techniques. You will be performing a minimal number of exercises and the benefits of lifting heavy will be transfered over more body parts with one compound lift. If you are on a volume program with lots of lifts and low frequency, consider using the technique that does not allow for the ancillary muscles to come into play or better yet choose an exercise that more directly targets the muscle that you are trying to develop.
